app: text field and callback

Signed-off-by: Vincent Batts <vbatts@hashbangbash.com>

src/helloworld/app.py

@@ -8,18 +8,33 @@ from toga.style.pack import COLUMN, ROW
 
 class HelloWorld(toga.App):
     def startup(self):
-        """Construct and show the Toga application.
+        main_box = toga.Box(style=Pack(direction=COLUMN))
 
-        Usually, you would add your application to a main content box.
-        We then create a main window (with a name matching the app), and
-        show the main window.
-        """
-        main_box = toga.Box()
+        name_label = toga.Label(
+                "Your name: ",
+                style=Pack(padding=(0, 5))
+                )
+        self.name_input = toga.TextInput(style=Pack(flex=1))
+
+        name_box = toga.Box(style=Pack(direction=ROW, padding=5))
+        name_box.add(name_label)
+        name_box.add(self.name_input)
+
+        button = toga.Button(
+                "Say Hello!",
+                on_press=self.say_hello,
+                style=Pack(padding=5)
+                )
+        main_box.add(name_box)
+        main_box.add(button)
 
         self.main_window = toga.MainWindow(title=self.formal_name)
         self.main_window.content = main_box
         self.main_window.show()
 
+    def say_hello(self, widget):
+        print(f"Hello, {self.name_input.value}")
+
 
 def main():
     return HelloWorld()